1. Field of the Invention
This invention relates to locks and has particular reference to electrically controlled door locks such as those controlled by a magnetically encoded card or a push button combination in which buttons must be pressed in a predetermined order to effect release of the lock.
2. Description of the Prior Art
Door locks, particularly of the key controlled type, are generally of standard size and fit in a standard size opening in a door. Thus, they are generally interchangeable.
On the other hand, electrically controlled door locks, are of particular advantage in high security situations, hotels, etc., where keys normally used to open the usual key locks, may be readily copied, or the locks may be readily picked, to enable unauthorized access to otherwise secure locations. However, such electrically controlled locks are generally quite bulky and are of a larger size than key controlled locks, requiring special size door lock openings, so that they are not easily interchangeable with key locks. Further, electrically controlled locks normally require relatively large power supplies thus rendering it impractical to provide a self contained lock unit with batteries incorporated therein, but require instead, electrical power from an external source with conductors leading to the lock unit.
In our copending applications, U.S. Pat. Nos. 4,754,625, issued on July 5, 1988 and 4,736,970, issued on Apr. 12, 1988. We have disclosed and claimed electrically controlled locks which require only relatively low powered electrical pulses for operation, using miniature or so called "AA" batteries or the like. This allows the lock unit to be interchangeable with a standard key lock.
Although such latter locks operate satisfactorily, they require electromagnets to effect the unlocking functions, and we have discovered that when the batteries have been discharged to a certain level, say 50% or less of their fully charged capacity, the resulting drop in voltage tends to make the electromagnets unreliable, apparently due to the relatively large magnetic gap between the pole pieces of the electromagents. We have further discovered that the use of a miniature electric motor in lieu of an electromagnet will enable the lock unit to be operated at much lower battery charge levels and thus tolerate a greater degree of exhaustion of the batteries before becoming unreliable. Certain other problems, however, are presented. For example, if the motor should become stalled due to advertent or inadvertent manipulating or holding of the lock release spindle knob by the operator, a heavy current drain of the batteries will ensue.
Accordingly, a principal object of the present invention is to provide a self contained electrically controlled lock unit which overcomes the above noted problems.
Another object is to provide an electrically controlled lock unit utilizing miniature batteries which can be reliably operated even when the batteries are appreciably discharged.
Another object is to provide an electrically controlled lock unit, utilizing an electric motor, which will fit within a standard size key lock door opening.
Another object is to provide an electrically operable control unit which can be incorporated in a commercially available door lock mechanism with a minimum amount of modification.
A further object is to provide an electrically controlled door lock unit which is simple and inexpensive to manufacture and install.
According to the invention, and in a door lock unit of the type comprising a pair of coaxially extending interior and exterior door knob spindles, each effective to actuate a lock bolt retractor independently of the other, a novel electrical lock control is provided comprising a locking pawl for one of the spindles. The pawl is driven between locking and unlocking positions by a miniature motor drive mechanism through an energy storing spring. The motor operates in one direction only and the mechanism operates through a cycle each time an actuating signal is received from a control device such as a magnetic card reader, a combination push button circuit or the like.
The cyclic drive mechanism operates through a split cycle, and during the first phase of the cycle, it normally actuates the pawl to an unlocking position but if the operator should attempt to rotate the knob spindle during such time, the pawl will usually be held in locking position by frictional engagement with the knob spindle but the drive mechanism will continue to operate through its first phase to a mid point of the cycle, storing energy in the spring without stalling the motor. At such time the motor will be deenergized and when the operator releases the knob spindle, the spring will become effective to move the lock pawl to unlocking position.
After a predetermined time period, the motor will again be energized to rotate in the same direction to actuate the drive mechanism through the second phase of its cycle to normally return the lock pawl to locking position. However, if the operator should hold the knob spindle in lock opening position during the second phase, the pawl will be prevented from moving into its locking position by the spindle but the drive mechanism will, nevertheless, continue to the end of its cycle without stalling the motor, thus storing engergy in the spring until the operator releases the knob spindle, whereupon the spring will return the pawl to locking position.